Mosasaur
A mother Mosasaur and her infants appear in Evolution's Winners. Physical Characteristics Along with plesiosaurs, sharks, fish, and other genera of mosasaurs, it was a dominant predator of the Western Interior Seaway during the Late Cretaceous. Tylosaurus proriger was among the largest of all the mosasaurs (along with Hainosaurus and Mosasaurus hoffmannii), reaching maximum lengths of 14 m (46 ft). A distinguishing characteristic of Tylosaurus is its elongated, cylindrical premaxilla (snout) from which it takes its name and which may have been used to ram and stun prey and also in intraspecific combat. Early restorations showing Tylosaurus with a dorsal crest were based on misidentified tracheal cartilage, but when the error was discovered, depicting mosasaurs with such crests was already a trend. Discovery Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two early Americanpaleontologists, Edward Drinker Cope and Othniel Charles Marsh. Originally, the name "Macrosaurus" proriger was proposed by Cope for a fragmentary skull and thirteen vertebrae collected from near Monument Rocks in western Kansas in 1868. It was placed in the collections of the Harvard Museum of Comparative Zoology. Only a year later, Cope redescribed the same material in greater detail and referred it, instead, to the English mosasaur taxon Liodon. Then, in 1872, Marsh named a more complete specimen as a new genus,Rhinosaurus ("nose lizard"), but soon discovered that this name had already been used for a different animal. Cope suggested that''Rhinosaurus'' be replaced by yet another new name, Rhamposaurus which also proved to be preoccupied. Marsh finally erected''Tylosaurus'' later in 1872, to include the original Harvard material as well as additional, more complete specimens which had also been collected from Kansas. A giant specimen of T. proriger, recovered in 1911 by C. D. Bunker near Wallace, Kansas is one of the largest skeleton of Tylosaurus ever found. It is currently on display at the University of Kansas Museum of Natural history. Paleobiology Stomach contents associated with specimens of Tylosaurus proriger indicate that this ferocious mosasaur had a varied diet, including fish, sharks, smaller mosasaurs, plesiosaurs, and flightless diving birds such as Hesperornis. In some paleoenvironments, Tylosaurus ''seems to have preferred shallow, nearshore waters (as with the Eutaw Formation and Mooreville Chalk Formation of Alabama), while favoring deeper water farther out from shore in other environments (as with the Niobrara Chalk of the western U.S.). The Talkeetna Mountains Hadrosaur was a hadrosaurid of indeterminate classification whose carcass appeared to have been deposited in a bathyal or outer shelf environment that later became Alaska's Matanuska Formation.Every element of its skeleton not found in aconcretion bore many closely spaced ovualar conical depressions ranging in diameter from 2.12 to 5.81 mm and 1.64 to 3.62 deep. These depressions are probably bite marks.The depressions are not symmetrical enough for gastropod drill marks and are not shaped likesponge borings. None of the preserved fish fossils of the Matanuska Formation fit the size or geometry of the borings. The size and spacing and shape by contrast, however, closely resembles the teeth of ''Tylosaurus proriger. The apparent tooth marks are unlikely to have occurred before the carcass was washed out to sea since that would have punctured the body, preventing the buildup of bloating gases that allowed the carcass to drift out to sea in the first place. The distribution of bite marks corresponds inversely to the presence of flesh in the animal. For instance, lower limb bones sustained the most damage because there was the least amount of flesh shielding the bones at those locations. The concretions formed as the flesh chemically reacted to the seafloor on the largest parts of the animal where the scavenging mosasaur would be unable to fully wrap its jaws around the carcass. Bones pulled free from the carcass were buried in the mud and preserved in mudstone. Gallery Tylo-2.jpg Category:Carnivores Category:Evolution's Winners animals Category:Cretaceous animals Category:Reptiles Category:Marine Reptile Category:Marine Animals Category:Non dinosaurs